This invention relates to in-situ vitrification of soil and particularly to a process for initiating in-situ vitrification.
The process of vitrifying soil, turning soil into a solid glassy substance, is accomplished as described by Brouns et al Patent No. 4,376,598 entitled "In-Situ Vitrification of Soil", by placing two electrodes in the soil and passing a substantial electric current through the electrodes and heating the soil until it melts. As the soil melts, it better conducts electricity thereby creating more heat and melting additional soil. When a sufficient volume of the soil reaches a molten state, the process is stopped and the soil is allowed to solidify. If gaseous by-products are released in the vitrification process, a dome with a filtering system can be positioned above the soil surface for containing and treating the gases. This process of soil vitrification is mainly used as an effective and cost efficient means for containing or stabilizing contaminated soil since turning the soil into a solid glasslike substance prevents chemical or radioactive contaminates from leaching out of the soil and contaminating the surrounding biosphere.
Soil in its solid state is a very poor conductor of electricity such that a start up procedure must be included in the process in order to initiate current flow. Once the heat generated by the current flow begins to melt the soil, the soil itself becomes a good conductor of electricity and perpetuates the melting process.
One prior art method of initiating the vitrification process involves placing a layer of graphite filings between the electrodes. In another method, a metal resistance coil is attached between the electrodes, and in yet a third method a chemical agent is employed to create a conductive path between the electrodes.
Each of the prior methods of initiating the vitrification process is subject to disadvantage. For example, when a layer of graphite filings is placed between the electrodes, a substantial amount of particulate matter is generated during initiation of the vitrification process. It is desirable to minimize the amount of particulate matter released during the vitrification process because the particles tend to clog the filter used in the gas treatment process thereby limiting the filter's effectiveness and decreasing its longevity. Additionally, unless a large quantity of graphite is used, the filing path is an unreliable electrical circuit providing inconsistent resistance and heat production which can cause arcing and electrical equipment failure. A need therefore exists for a start-up method that will provide a reliable electrical path with consistent resistance and temperature properties while not generating excessive particulate matter.